 # Chapter 7 Electricity Section 1 Electric Charge Static

• Slides: 33 Chapter 7 Electricity Section 1 Electric Charge Static Electricity � Accumulation of excess electric charge � As you walk across the carpet, electrons are transferred from the carpet to your shoes � Your shoes become negatively charged � The carpet becomes positively charged Law of Conservation of Charge � Charge can be transferred from object to object, but it cannot be created or destroyed. � Usually place the electrons move from place to Forces and Electric Charge � “Like” charges repel � “Unlike” � This charges attract is why clothes from the dryer stick together due to the transfer of electrons Electric Fields � There is an electric field around every electric charge � Example: Being shocked when you reach for a doorknob but do not actually touch it Conductors and Insulators � Conductors- electrons move through easily Ex: Metals � Insulator- electrons do not move through this material easily Ex: Plastics Charging Objects � Charging by contact- charge is transferred by touching or rubbing � Charging by induction- charges are rearranged on a neutral object due to a nearby charged object Explain why if charge cannot be created or destroyed, electrically neutral objects can become electrically charged. Humid air is a better electrical conductor than dry air. Explain why you’re more likely to receive a shock after walking across a carpet when the air is dry than when the air is humid. Chapter 7 Electricity Section 2 Electric Current Electric Current � This is the flow of electrons � Measured � The in amperes; amps rate that the electrons move through a conductor. Voltage Difference � Related to the force that causes electric charges to flow � Measured in volts; V Voltage � Electric Charge flows from higher voltage to lower voltage A. K. A. : � Potential Difference- the work that must be done to move a charge from one place to another Circuit � Closed path that current flows through � Current will only flow on a closed path Resistance � How much a material opposes the flow of electrons � Measured in ohms; Ω Resistance � Temperature � Length � Thickness *When these increase so does resistance Ohm’s Law � Equation Current = voltage difference resistance or I= V R Example Calculate the voltage difference in a circuit with a resistance of 25Ω if the current in the circuit is 0. 5 A. Example A current of 0. 5 A flows in a 60 W light bulb when the voltage difference between the ends of the filament is 120 V. What is the resistance of the filament? Chapter 7 Electricity Section 3 Electrical Energy Closed vs. Open Circuit � Closed � Open Circuit: Charge can flow uninterrupted Circuit: Charge cannot flow; circuit is broken When one bulb is out in a string of lights, why do the rest not work? ? Circuits � Switch- used to open and close a circuit - Ex: Light switch in your home � Schematic Diagram- a diagram that depicts the construction of an electrical circuit or apparatus Series Circuit � The current can only flow through one loop � Used in flashlights and holiday lights Parallel Circuits � These have two or more circuits the current can move through � Used in houses and automobiles � Useful because unlike series circuits, individual parts can be turned off without affecting the entire circuit Household Circuits � If too much current flows through the wires, they will overheat and melt which can cause a fire � To protect against this fuses and circuit breakers are used Fuses � These contain a small piece of metal that will melt if it becomes too hot � This causes a break in the circuit which stops the flow of current � You must replace these with new ones Circuit Breaker � Contains a piece of metal that bends when it overheats � The bending causes a switch to flip which opens the circuit and stops the current flow � These may be reset by flipping the switch Electric Power � How fast electrical energy is converted to another type of energy � This etc. can be thermal, light, mechanical energy Electrical Power Equation Electric power = current X voltage difference P= I(V) *Measured in watts; W *One kilowatt (k. W) = 1, 000 watts Example The current in an electric clothes dryer is 15 A when it is plugged into a 240 volt outlet. How much power does the clothes dryer use? Electrical Energy � Measured � Equation: in kilowatt hours (k. Wh) Electrical energy = electric power X time or E= Pt Example A microwave oven with a power rating of 1, 200 W is used for 0. 25 h. How much electrical energy is used by the microwave?